patch-2.2.5 linux/drivers/char/n_hdlc.c

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diff -u --recursive --new-file v2.2.4/linux/drivers/char/n_hdlc.c linux/drivers/char/n_hdlc.c
@@ -0,0 +1,1151 @@
+/* generic HDLC line discipline for Linux
+ *
+ * Written by Paul Fulghum paulkf@microgate.com
+ * for Microgate Corporation
+ *
+ * Microgate and SyncLink are registered trademarks of Microgate Corporation
+ *
+ * Adapted from ppp.c, written by Michael Callahan <callahan@maths.ox.ac.uk>,
+ *	Al Longyear <longyear@netcom.com>, Paul Mackerras <Paul.Mackerras@cs.anu.edu.au>
+ *
+ * Original release 01/11/99
+ *
+ * This code is released under the GNU General Public License (GPL)
+ *
+ * This module implements the tty line discipline N_HDLC for use with
+ * tty device drivers that support bit-synchronous HDLC communications.
+ *
+ * All HDLC data is frame oriented which means:
+ *
+ * 1. tty write calls represent one complete transmit frame of data
+ *    The device driver should accept the complete frame or none of 
+ *    the frame (busy) in the write method. Each write call should have
+ *    a byte count in the range of 2-4096 bytes (2 is min HDLC frame
+ *    with 1 addr byte and 1 ctrl byte).
+ *
+ * 2. receive callbacks from the device driver represents
+ *    one received frame. The device driver should bypass
+ *    the tty flip buffer and call the line discipline receive
+ *    callback directly to avoid fragmenting or concatenating
+ *    multiple frames into a single receive callback.
+ *
+ *    The HDLC line discipline queues the receive frames in seperate
+ *    buffers so complete receive frames can be returned by the
+ *    tty read calls.
+ *
+ * 3. tty read calls returns an entire frame of data or nothing.
+ *    
+ * 4. all send and receive data is considered raw. No processing
+ *    or translation is performed by the line discipline, regardless
+ *    of the tty flags
+ *
+ * 5. When line discipline is queried for the amount of receive
+ *    data available (FIOC), 0 is returned if no data available,
+ *    otherwise the count of the next available frame is returned.
+ *    (instead of the sum of all received frame counts).
+ *
+ * These conventions allow the standard tty programming interface
+ * to be used for synchronous HDLC applications when used with
+ * this line discipline (or another line discipline that is frame
+ * oriented such as N_PPP).
+ *
+ * The SyncLink driver (synclink.c) implements both asynchronous
+ * (using standard line discipline N_TTY) and synchronous HDLC
+ * (using N_HDLC) communications, with the latter using the above
+ * conventions.
+ *
+ * This implementation is very basic and does not maintain
+ * any statistics. The main point is to enforce the raw data
+ * and frame orientation of HDLC communications.
+ *
+ * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
+ * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,
+ * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#define HDLC_MAGIC 0x239e
+#define HDLC_VERSION "1.0"
+
+#include <linux/version.h>
+#include <linux/config.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/types.h>
+#include <linux/fcntl.h>
+#include <linux/interrupt.h>
+#include <linux/ptrace.h>
+
+#undef VERSION
+#define VERSION(major,minor,patch) (((((major)<<8)+(minor))<<8)+(patch))
+
+#if LINUX_VERSION_CODE < VERSION(2,1,14)
+#include <linux/ioport.h>
+#endif
+
+#if LINUX_VERSION_CODE >= VERSION(2,1,23)
+#include <linux/poll.h>
+#endif
+
+#include <linux/in.h>
+#include <linux/malloc.h>
+#include <linux/tty.h>
+#include <linux/errno.h>
+#include <linux/sched.h>	/* to get the struct task_struct */
+#include <linux/string.h>	/* used in new tty drivers */
+#include <linux/signal.h>	/* used in new tty drivers */
+#include <asm/system.h>
+#include <asm/bitops.h>
+#include <asm/termios.h>
+#include <linux/if.h>
+
+#include <linux/ioctl.h>
+
+#ifdef CONFIG_KERNELD
+#include <linux/kerneld.h>
+#endif
+
+#if LINUX_VERSION_CODE >= VERSION(2,1,4)
+#include <asm/segment.h>
+#define GET_USER(error,value,addr) error = get_user(value,addr)
+#define COPY_FROM_USER(error,dest,src,size) error = copy_from_user(dest,src,size) ? -EFAULT : 0
+#define PUT_USER(error,value,addr) error = put_user(value,addr)
+#define COPY_TO_USER(error,dest,src,size) error = copy_to_user(dest,src,size) ? -EFAULT : 0
+
+#if LINUX_VERSION_CODE >= VERSION(2,1,5)
+#include <asm/uaccess.h>
+#endif
+
+#else  /* 2.0.x and 2.1.x before 2.1.4 */
+
+#define GET_USER(error,value,addr)					  \
+do {									  \
+	error = verify_area (VERIFY_READ, (void *) addr, sizeof (value)); \
+	if (error == 0)							  \
+		value = get_user(addr);					  \
+} while (0)
+
+#define COPY_FROM_USER(error,dest,src,size)				  \
+do {									  \
+	error = verify_area (VERIFY_READ, (void *) src, size);		  \
+	if (error == 0)							  \
+		memcpy_fromfs (dest, src, size);			  \
+} while (0)
+
+#define PUT_USER(error,value,addr)					   \
+do {									   \
+	error = verify_area (VERIFY_WRITE, (void *) addr, sizeof (value)); \
+	if (error == 0)							   \
+		put_user (value, addr);					   \
+} while (0)
+
+#define COPY_TO_USER(error,dest,src,size)				  \
+do {									  \
+	error = verify_area (VERIFY_WRITE, (void *) dest, size);		  \
+	if (error == 0)							  \
+		memcpy_tofs (dest, src, size);				  \
+} while (0)
+
+#endif
+
+#if LINUX_VERSION_CODE < VERSION(2,1,0)
+#define __init
+typedef int spinlock_t;
+#define spin_lock_irqsave(a,b) {save_flags((b));cli();}
+#define spin_unlock_irqrestore(a,b) {restore_flags((b));}
+#define spin_lock(a)
+#define spin_unlock(a)
+#define schedule_timeout(a){current->timeout = jiffies + (a); schedule();}
+#endif
+
+#if LINUX_VERSION_CODE < VERSION(2,1,37)
+#define test_and_set_bit(nr, addr)	set_bit(nr, addr)
+#endif
+
+#if LINUX_VERSION_CODE < VERSION(2,1,57)
+#define signal_pending(p)	((p)->signal & ~(p)->blocked)
+#endif
+
+#if LINUX_VERSION_CODE < VERSION(2,1,25)
+#define net_device_stats	enet_statistics
+#endif
+
+#if LINUX_VERSION_CODE < VERSION(2,1,60)
+typedef int		rw_ret_t;
+typedef unsigned int	rw_count_t;
+#else
+typedef ssize_t		rw_ret_t;
+typedef size_t		rw_count_t;
+#endif
+
+/*
+ * Buffers for individual HDLC frames
+ */
+#define MAX_HDLC_FRAME_SIZE 4096
+#define DEFAULT_RX_BUF_COUNT 10
+#define MAX_RX_BUF_COUNT 30
+#define DEFAULT_TX_BUF_COUNT 1
+
+typedef struct _n_hdlc_buf
+{
+	struct _n_hdlc_buf *link;
+	int count;
+	char buf[MAX_HDLC_FRAME_SIZE];
+} N_HDLC_BUF;
+
+typedef struct _n_hdlc_buf_list
+{
+	N_HDLC_BUF *head;
+	N_HDLC_BUF *tail;
+	int count;
+	spinlock_t spinlock;
+	
+} N_HDLC_BUF_LIST;
+
+/*
+ * Per device instance data structure
+ */
+struct n_hdlc {
+	int		magic;		/* magic value for structure	*/
+	__u32		flags;		/* miscellaneous control flags	*/
+	
+	struct tty_struct *tty;		/* ptr to TTY structure	*/
+	struct tty_struct *backup_tty;	/* TTY to use if tty gets closed */
+	
+	/* Queues for select() functionality */
+	struct wait_queue *read_wait;
+	struct wait_queue *write_wait;
+
+	int		tbusy;		/* reentrancy flag for tx wakeup code */
+	int		woke_up;
+	N_HDLC_BUF	*tbuf;		/* currently transmitting tx buffer */
+	N_HDLC_BUF_LIST tx_buf_list;	/* list of pending transmit frame buffers */	
+	N_HDLC_BUF_LIST	rx_buf_list;	/* list of received frame buffers */
+	N_HDLC_BUF_LIST tx_free_buf_list;	/* list unused transmit frame buffers */	
+	N_HDLC_BUF_LIST	rx_free_buf_list;	/* list unused received frame buffers */
+};
+
+/*
+ * HDLC buffer list manipulation functions
+ */
+void n_hdlc_buf_list_init(N_HDLC_BUF_LIST *list);
+void n_hdlc_buf_put(N_HDLC_BUF_LIST *list,N_HDLC_BUF *buf);
+N_HDLC_BUF* n_hdlc_buf_get(N_HDLC_BUF_LIST *list);
+
+/* Local functions */
+
+static struct n_hdlc *n_hdlc_alloc (void);
+
+#if LINUX_VERSION_CODE >= VERSION(2,1,19) 
+MODULE_PARM(debuglevel, "i");
+#endif
+
+/* debug level can be set by insmod for debugging purposes */
+#define DEBUG_LEVEL_INFO	1
+int debuglevel=0;
+
+/* TTY callbacks */
+
+static rw_ret_t n_hdlc_tty_read(struct tty_struct *,
+	struct file *, __u8 *, rw_count_t);
+static rw_ret_t n_hdlc_tty_write(struct tty_struct *,
+	struct file *, const __u8 *, rw_count_t);
+static int n_hdlc_tty_ioctl(struct tty_struct *,
+	struct file *, unsigned int, unsigned long);
+#if LINUX_VERSION_CODE < VERSION(2,1,23)
+static int n_hdlc_tty_select (struct tty_struct *tty, struct inode *inode,
+		      struct file *filp, int sel_type, select_table * wait);
+#else
+static unsigned int n_hdlc_tty_poll (struct tty_struct *tty, struct file *filp,
+				  poll_table * wait);
+#endif
+static int n_hdlc_tty_open (struct tty_struct *);
+static void n_hdlc_tty_close (struct tty_struct *);
+static int n_hdlc_tty_room (struct tty_struct *tty);
+static void n_hdlc_tty_receive (struct tty_struct *tty,
+	const __u8 * cp, char *fp, int count);
+static void n_hdlc_tty_wakeup (struct tty_struct *tty);
+
+#define bset(p,b)	((p)[(b) >> 5] |= (1 << ((b) & 0x1f)))
+
+#define tty2n_hdlc(tty)	((struct n_hdlc *) ((tty)->disc_data))
+#define n_hdlc2tty(n_hdlc)	((n_hdlc)->tty)
+
+/* Define this string only once for all macro invocations */
+static char szVersion[] = HDLC_VERSION;
+
+/* n_hdlc_release()
+ *
+ *	release an n_hdlc per device line discipline info structure
+ *
+ */
+static void n_hdlc_release (struct n_hdlc *n_hdlc)
+{
+	struct tty_struct *tty = n_hdlc2tty (n_hdlc);
+	N_HDLC_BUF *buf;
+	
+	if (debuglevel >= DEBUG_LEVEL_INFO)	
+		printk("%s(%d)n_hdlc_release() called\n",__FILE__,__LINE__);
+		
+	/* Ensure that the n_hdlcd process is not hanging on select()/poll() */
+	wake_up_interruptible (&n_hdlc->read_wait);
+	wake_up_interruptible (&n_hdlc->write_wait);
+
+	if (tty != NULL && tty->disc_data == n_hdlc)
+		tty->disc_data = NULL;	/* Break the tty->n_hdlc link */
+
+	/* Release transmit and receive buffers */
+	for(;;) {
+		buf = n_hdlc_buf_get(&n_hdlc->rx_free_buf_list);
+		if (buf) {
+			kfree(buf);
+		} else
+			break;
+	}
+	for(;;) {
+		buf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list);
+		if (buf) {
+			kfree(buf);
+		} else
+			break;
+	}
+	for(;;) {
+		buf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
+		if (buf) {
+			kfree(buf);
+		} else
+			break;
+	}
+	for(;;) {
+		buf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
+		if (buf) {
+			kfree(buf);
+		} else
+			break;
+	}
+	
+	kfree(n_hdlc);
+	
+}	/* end of n_hdlc_release() */
+
+/* n_hdlc_tty_close()
+ *
+ *	Called when the line discipline is changed to something
+ *	else, the tty is closed, or the tty detects a hangup.
+ */
+static void n_hdlc_tty_close(struct tty_struct *tty)
+{
+	struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
+
+	if (debuglevel >= DEBUG_LEVEL_INFO)	
+		printk("%s(%d)n_hdlc_tty_close() called\n",__FILE__,__LINE__);
+		
+	if (n_hdlc != NULL) {
+		if (n_hdlc->magic != HDLC_MAGIC) {
+			printk (KERN_WARNING"n_hdlc: trying to close unopened tty!\n");
+			return;
+		}
+		tty->disc_data = NULL;
+		if (tty == n_hdlc->backup_tty)
+			n_hdlc->backup_tty = 0;
+		if (tty != n_hdlc->tty)
+			return;
+		if (n_hdlc->backup_tty) {
+			n_hdlc->tty = n_hdlc->backup_tty;
+		} else {
+			n_hdlc_release (n_hdlc);
+			MOD_DEC_USE_COUNT;
+		}
+	}
+	
+	if (debuglevel >= DEBUG_LEVEL_INFO)	
+		printk("%s(%d)n_hdlc_tty_close() success\n",__FILE__,__LINE__);
+		
+}	/* end of n_hdlc_tty_close() */
+
+/* n_hdlc_tty_open
+ * 
+ * 	called when line discipline changed to n_hdlc
+ * 	
+ * Arguments:	tty	pointer to tty info structure
+ * Return Value:	0 if success, otherwise error code
+ */
+static int n_hdlc_tty_open (struct tty_struct *tty)
+{
+	struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
+
+	if (debuglevel >= DEBUG_LEVEL_INFO)	
+		printk("%s(%d)n_hdlc_tty_open() called\n",__FILE__,__LINE__);
+		
+	/* There should not be an existing table for this slot. */
+	if (n_hdlc) {
+		printk (KERN_ERR"n_hdlc_tty_open:tty already associated!\n" );
+		return -EEXIST;
+	}
+	
+	n_hdlc = n_hdlc_alloc();
+	if (!n_hdlc) {
+		printk (KERN_ERR "n_hdlc_alloc failed\n");
+		return -ENFILE;
+	}
+		
+	tty->disc_data = n_hdlc;
+	n_hdlc->tty    = tty;
+		
+	MOD_INC_USE_COUNT;
+	
+	/* Flush any pending characters in the driver and discipline. */
+	
+	if (tty->ldisc.flush_buffer)
+		tty->ldisc.flush_buffer (tty);
+
+	if (tty->driver.flush_buffer)
+		tty->driver.flush_buffer (tty);
+		
+	if (debuglevel >= DEBUG_LEVEL_INFO)	
+		printk("%s(%d)n_hdlc_tty_open() success\n",__FILE__,__LINE__);
+		
+	return 0;
+	
+}	/* end of n_tty_hdlc_open() */
+
+/* n_hdlc_send_frames()
+ * 
+ * 	send frames on pending send buffer list until the
+ * 	driver does not accept a frame (busy)
+ * 	this function is called after adding a frame to the
+ * 	send buffer list and by the tty wakeup callback
+ * 	
+ * Arguments:		n_hdlc		pointer to ldisc instance data
+ * 			tty		pointer to tty instance data
+ * Return Value:	None
+ */
+static void n_hdlc_send_frames (struct n_hdlc *n_hdlc, struct tty_struct *tty)
+{
+	register int actual;
+	unsigned long flags;
+	N_HDLC_BUF *tbuf;
+	
+	if (debuglevel >= DEBUG_LEVEL_INFO)	
+		printk("%s(%d)n_hdlc_send_frames() called\n",__FILE__,__LINE__);
+		
+	save_flags(flags);
+	cli ();
+	if (n_hdlc->tbusy) {
+		n_hdlc->woke_up = 1;
+		restore_flags(flags);
+		return;
+	}
+	n_hdlc->tbusy = 1;
+	restore_flags(flags);
+
+	/* get current transmit buffer or get new transmit */
+	/* buffer from list of pending transmit buffers */
+		
+	tbuf = n_hdlc->tbuf;
+	if (!tbuf)
+		tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
+		
+	while (tbuf) {
+		if (debuglevel >= DEBUG_LEVEL_INFO)	
+			printk("%s(%d)sending frame %p, count=%d\n",
+				__FILE__,__LINE__,tbuf,tbuf->count);
+			
+		/* Send the next block of data to device */
+		n_hdlc->woke_up = 0;
+		tty->flags |= (1 << TTY_DO_WRITE_WAKEUP);
+		actual = tty->driver.write(tty, 0, tbuf->buf, tbuf->count);
+		    
+		/* if transmit error, throw frame away by */
+		/* pretending it was accepted by driver */
+		if (actual < 0)
+			actual = tbuf->count;
+		
+		if (actual == tbuf->count) {
+			if (debuglevel >= DEBUG_LEVEL_INFO)	
+				printk("%s(%d)frame %p completed\n",
+					__FILE__,__LINE__,tbuf);
+					
+			/* free current transmit buffer */
+			n_hdlc_buf_put(&n_hdlc->tx_free_buf_list,tbuf);
+			
+			/* this tx buffer is done */
+			n_hdlc->tbuf = NULL;
+			
+			/* wait up sleeping writers */
+			wake_up_interruptible(&n_hdlc->write_wait);
+	
+			/* get next pending transmit buffer */
+			tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
+		} else {
+			if (debuglevel >= DEBUG_LEVEL_INFO)	
+				printk("%s(%d)frame %p pending\n",
+					__FILE__,__LINE__,tbuf);
+					
+			/* buffer not accepted by driver */
+			
+			/* check if wake up code called since last write call */
+			if (n_hdlc->woke_up)
+				continue;
+				
+			/* set this buffer as pending buffer */
+			n_hdlc->tbuf = tbuf;
+			break;
+		}
+	}
+	
+	if (!tbuf)
+		tty->flags  &= ~(1 << TTY_DO_WRITE_WAKEUP);
+	
+	/* Clear the re-entry flag */
+	save_flags(flags);
+	cli ();
+	n_hdlc->tbusy = 0;
+	restore_flags(flags);
+	
+	if (debuglevel >= DEBUG_LEVEL_INFO)	
+		printk("%s(%d)n_hdlc_send_frames() exit\n",__FILE__,__LINE__);
+		
+}	/* end of n_hdlc_send_frames() */
+
+/* n_hdlc_tty_wakeup()
+ *
+ *	Callback for transmit wakeup. Called when low level
+ *	device driver can accept more send data.
+ *
+ * Arguments:		tty	pointer to associated tty instance data
+ * Return Value:	None
+ */
+static void n_hdlc_tty_wakeup (struct tty_struct *tty)
+{
+	struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
+
+	if (debuglevel >= DEBUG_LEVEL_INFO)	
+		printk("%s(%d)n_hdlc_tty_wakeup() called\n",__FILE__,__LINE__);
+		
+	if (!n_hdlc)
+		return;
+
+	if (tty != n_hdlc->tty) {
+		tty->flags &= ~(1 << TTY_DO_WRITE_WAKEUP);
+		return;
+	}
+	
+	if (!n_hdlc->tbuf)
+		tty->flags &= ~(1 << TTY_DO_WRITE_WAKEUP);
+	else
+		n_hdlc_send_frames (n_hdlc, tty);
+		
+}	/* end of n_hdlc_tty_wakeup() */
+
+/* n_hdlc_tty_room()
+ * 
+ *	Callback function from tty driver. Return the amount of 
+ *	space left in the receiver's buffer to decide if remote
+ *	transmitter is to be throttled.
+ *
+ * Arguments:		tty	pointer to associated tty instance data
+ * Return Value:	number of bytes left in receive buffer
+ */
+static int n_hdlc_tty_room (struct tty_struct *tty)
+{
+	if (debuglevel >= DEBUG_LEVEL_INFO)	
+		printk("%s(%d)n_hdlc_tty_room() called\n",__FILE__,__LINE__);
+	/* always return a larger number to prevent */
+	/* throttling of remote transmitter. */
+	return 65536;
+}	/* end of n_hdlc_tty_root() */
+
+/* n_hdlc_tty_receive()
+ * 
+ * 	Called by tty low level driver when receive data is
+ * 	available. Data is interpreted as one HDLC frame.
+ * 	
+ * Arguments:	 	tty		pointer to tty isntance data
+ * 			data		pointer to received data
+ * 			flags		pointer to flags for data
+ * 			count		count of received data in bytes
+ * 	
+ * Return Value:	None
+ */
+static void n_hdlc_tty_receive(struct tty_struct *tty,
+	const __u8 * data, char *flags, int count)
+{
+	register struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
+	register N_HDLC_BUF *buf;
+
+	if (debuglevel >= DEBUG_LEVEL_INFO)	
+		printk("%s(%d)n_hdlc_tty_receive() called count=%d\n",
+			__FILE__,__LINE__, count);
+		
+	/* This can happen if stuff comes in on the backup tty */
+	if (n_hdlc == 0 || tty != n_hdlc->tty)
+		return;
+		
+	/* verify line is using HDLC discipline */
+	if (n_hdlc->magic != HDLC_MAGIC) {
+		printk("%s(%d) line not using HDLC discipline\n",
+			__FILE__,__LINE__);
+		return;
+	}
+	
+	/* get a free HDLC buffer */	
+	buf = n_hdlc_buf_get(&n_hdlc->rx_free_buf_list);
+	if (!buf) {
+		/* no buffers in free list, attempt to allocate another rx buffer */
+		/* unless the maximum count has been reached */
+		if (n_hdlc->rx_buf_list.count < MAX_RX_BUF_COUNT)
+			buf = (N_HDLC_BUF*)kmalloc(sizeof(N_HDLC_BUF),GFP_ATOMIC);
+	}
+	
+	if (!buf) {
+		printk("%s(%d) no more rx buffers, data discarded\n",
+			__FILE__,__LINE__);
+		return;
+	}
+		
+	/* copy received data to HDLC buffer */
+	memcpy(buf->buf,data,count);
+	buf->count=count;
+
+	/* add HDLC buffer to list of received frames */
+	n_hdlc_buf_put(&n_hdlc->rx_buf_list,buf);
+	
+	/* wake up any blocked reads and perform async signalling */
+	wake_up_interruptible (&n_hdlc->read_wait);
+	if (n_hdlc->tty->fasync != NULL)
+		kill_fasync (n_hdlc->tty->fasync, SIGIO);
+
+}	/* end of n_hdlc_tty_receive() */
+
+/* n_hdlc_tty_read()
+ * 
+ * 	Called to retreive one frame of data (if available)
+ * 	
+ * Arguments:
+ * 
+ * 	tty		pointer to tty instance data
+ * 	file		pointer to open file object
+ * 	buf		pointer to returned data buffer
+ * 	nr		size of returned data buffer
+ * 	
+ * Return Value:
+ * 
+ * 	Number of bytes returned or error code
+ */
+static rw_ret_t n_hdlc_tty_read (struct tty_struct *tty,
+	struct file *file, __u8 * buf, rw_count_t nr)
+{
+	struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
+	int error;
+	rw_ret_t ret;
+	N_HDLC_BUF *rbuf;
+
+	if (debuglevel >= DEBUG_LEVEL_INFO)	
+		printk("%s(%d)n_hdlc_tty_read() called\n",__FILE__,__LINE__);
+		
+	/* Validate the pointers */
+	if (!n_hdlc)
+		return -EIO;
+
+	/* verify user access to buffer */
+	error = verify_area (VERIFY_WRITE, buf, nr);
+	if (error != 0) {
+		printk(KERN_WARNING"%s(%d) n_hdlc_tty_read() can't verify user "
+		"buffer\n",__FILE__,__LINE__);
+		return (error);
+	}
+
+	for (;;) {
+		n_hdlc = tty2n_hdlc (tty);
+		if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC ||
+			 tty != n_hdlc->tty)
+			return 0;
+
+		rbuf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
+		if (rbuf)
+			break;
+			
+		/* no data */
+		if (file->f_flags & O_NONBLOCK)
+			return -EAGAIN;
+			
+		/* TODO: no timeout? current->timeout = 0;*/
+		interruptible_sleep_on (&n_hdlc->read_wait);
+		if (signal_pending(current))
+			return -EINTR;
+	}
+
+	if (rbuf->count > nr) {
+		/* frame too large for caller's buffer (discard frame) */
+		ret = (rw_ret_t)-EOVERFLOW;
+	} else {
+		/* Copy the data to the caller's buffer */
+		COPY_TO_USER(error,buf,rbuf->buf,rbuf->count);
+		if (error)
+			ret = (rw_ret_t)error;
+		else
+			ret = (rw_ret_t)rbuf->count;
+	}
+	
+	/* return HDLC buffer to free list unless the free list */
+	/* count has exceeded the default value, in which case the */
+	/* buffer is freed back to the OS to conserve memory */
+	if (n_hdlc->rx_free_buf_list.count > DEFAULT_RX_BUF_COUNT)
+		kfree(rbuf);
+	else	
+		n_hdlc_buf_put(&n_hdlc->rx_free_buf_list,rbuf);
+	
+	return ret;
+	
+}	/* end of n_hdlc_tty_read() */
+
+/* n_hdlc_tty_write()
+ * 
+ * 	write a single frame of data to device
+ * 	
+ * Arguments:	tty	pointer to associated tty device instance data
+ * 		file	pointer to file object data
+ * 		data	pointer to transmit data (one frame)
+ * 		count	size of transmit frame in bytes
+ * 		
+ * Return Value:	number of bytes written (or error code)
+ */
+static rw_ret_t n_hdlc_tty_write (struct tty_struct *tty, struct file *file,
+	const __u8 * data, rw_count_t count)
+{
+	struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
+	int error = 0;
+	struct wait_queue wait = {current, NULL};
+	N_HDLC_BUF *tbuf;
+
+	if (debuglevel >= DEBUG_LEVEL_INFO)	
+		printk("%s(%d)n_hdlc_tty_write() called count=%d\n",
+			__FILE__,__LINE__,count);
+		
+	/* Verify pointers */
+	if (!n_hdlc)
+		return -EIO;
+
+	if (n_hdlc->magic != HDLC_MAGIC)
+		return -EIO;
+
+	/* verify frame size */
+	if (count > MAX_HDLC_FRAME_SIZE) {
+		if (debuglevel & DEBUG_LEVEL_INFO)
+			printk (KERN_WARNING
+				"n_hdlc_tty_write: truncating user packet "
+				"from %lu to %d\n", (unsigned long) count,
+				MAX_HDLC_FRAME_SIZE);
+		count = MAX_HDLC_FRAME_SIZE;
+	}
+	
+	/* Allocate transmit buffer */
+	tbuf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list);
+	if (!tbuf) {
+		/* sleep until transmit buffer available */		
+		add_wait_queue(&n_hdlc->write_wait, &wait);
+		while (!tbuf) {
+			/* TODO: no timeout? current->timeout = 0;*/
+			current->state = TASK_INTERRUPTIBLE;
+			schedule();
+
+			n_hdlc = tty2n_hdlc (tty);
+			if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC || 
+			    tty != n_hdlc->tty) {
+				printk("n_hdlc_tty_write: %p invalid after wait!\n", n_hdlc);
+				error = -EIO;
+				break;
+			}
+			
+			if (signal_pending(current)) {
+				error = -EINTR;
+				break;
+			}
+			
+			tbuf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list);
+		}
+		current->state = TASK_RUNNING;
+		remove_wait_queue(&n_hdlc->write_wait, &wait);
+	}
+
+	if (!error) {		
+		/* Retrieve the user's buffer */
+		COPY_FROM_USER (error, tbuf->buf, data, count);
+		if (error) {
+			/* return tx buffer to free list */
+			n_hdlc_buf_put(&n_hdlc->tx_free_buf_list,tbuf);
+		} else {
+			/* Send the data */
+			tbuf->count = error = count;
+			n_hdlc_buf_put(&n_hdlc->tx_buf_list,tbuf);
+			n_hdlc_send_frames(n_hdlc,tty);
+		}
+	}
+
+	return error;
+	
+}	/* end of n_hdlc_tty_write() */
+
+/* n_hdlc_tty_ioctl()
+ *
+ *	Process IOCTL system call for the tty device.
+ *
+ * Arguments:
+ *
+ *	tty		pointer to tty instance data
+ *	file		pointer to open file object for device
+ *	cmd		IOCTL command code
+ *	arg		argument for IOCTL call (cmd dependent)
+ *
+ * Return Value:	Command dependent
+ */
+static int n_hdlc_tty_ioctl (struct tty_struct *tty, struct file * file,
+               unsigned int cmd, unsigned long arg)
+{
+	struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
+	int error = 0;
+	
+	if (debuglevel >= DEBUG_LEVEL_INFO)	
+		printk("%s(%d)n_hdlc_tty_ioctl() called %d\n",
+			__FILE__,__LINE__,cmd);
+		
+	/* Verify the status of the device */
+	if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC)
+		return -EBADF;
+
+	switch (cmd) {
+	case FIONREAD:
+		{
+			/* report count of read data available */
+			/* in next available frame (if any) */
+			int count;
+			unsigned long flags;
+			spin_lock_irqsave(&n_hdlc->rx_buf_list.spinlock,flags);
+			if (n_hdlc->rx_buf_list.head)
+				count = n_hdlc->rx_buf_list.head->count;
+			else
+				count = 0;
+			spin_unlock_irqrestore(&n_hdlc->rx_buf_list.spinlock,flags);
+			PUT_USER (error, count, (int *) arg);
+		}
+		break;
+		
+	default:
+		error = n_tty_ioctl (tty, file, cmd, arg);
+		break;
+	}
+	return error;
+	
+}	/* end of n_hdlc_tty_ioctl() */
+
+#if LINUX_VERSION_CODE < VERSION(2,1,23)
+/* n_hdlc_tty_select()
+ * 
+ * 	Device select method. Determine if operation requires
+ * 	blocking and if so put appropriate wait queue in select
+ * 	table and return 0, otherwise return 1.
+ * 	
+ * Arguments:
+ * 
+ * 	tty		pointer to tty device instance data
+ * 	inode		pointer to inode for device
+ * 	filp		pointer to file object
+ * 	sel_type	identified the select type (read/write/exception)
+ * 	wait		select table for adding wait queue if appropriate
+ * 	
+ * Return Value:
+ * 
+ * 	1 if no need to block on operation
+ * 	0 if must block and wait queue added to select table
+ */
+static int n_hdlc_tty_select (struct tty_struct *tty, struct inode *inode,
+		struct file *filp, int sel_type, select_table * wait)
+{
+	struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
+	int result = 1;
+	
+	if (debuglevel >= DEBUG_LEVEL_INFO)	
+		printk("%s(%d)n_hdlc_tty_select() called\n",__FILE__,__LINE__);
+		
+	/* Verify the status of the device */
+	if (!n_hdlc)
+		return -EBADF;
+
+	if (n_hdlc->magic != HDLC_MAGIC || tty != n_hdlc->tty)
+		return -EBADF;
+
+	switch (sel_type) {
+	case SEL_IN:
+		if (n_hdlc->rx_buf_list.head)
+			break;
+
+	case SEL_EX:	/* Exceptions or read errors */
+		/* Is this a pty link and the remote disconnected? */
+		if (tty->flags & (1 << TTY_OTHER_CLOSED))
+			break;
+
+		/* Is this a local link and the modem disconnected? */
+		if (tty_hung_up_p (filp))
+			break;
+
+		select_wait (&n_hdlc->read_wait, wait);
+		result = 0;
+		break;
+		
+	/* Write mode. A write is allowed if there is no current transmission */
+	case SEL_OUT:
+		if (!n_hdlc->tx_free_buf_list.head) {
+			select_wait (&n_hdlc->write_wait, wait);
+			result = 0;
+		}
+		break;
+	}
+	return result;
+}	/* end of n_hdlc_tty_select() */
+
+#else	/* 2.1.23 or later */
+
+/* n_hdlc_tty_poll()
+ * 
+ * 	TTY callback for poll system call. Determine which 
+ * 	operations (read/write) will not block and return
+ * 	info to caller.
+ * 	
+ * Arguments:
+ * 
+ * 	tty		pointer to tty instance data
+ * 	filp		pointer to open file object for device
+ * 	poll_table	wait queue for operations
+ * 
+ * Return Value:
+ * 
+ * 	bit mask containing info on which ops will not block
+ */
+static unsigned int n_hdlc_tty_poll (struct tty_struct *tty,
+	 struct file *filp, poll_table * wait)
+{
+	struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
+	unsigned int mask = 0;
+
+	if (debuglevel >= DEBUG_LEVEL_INFO)	
+		printk("%s(%d)n_hdlc_tty_poll() called\n",__FILE__,__LINE__);
+		
+	if (n_hdlc && n_hdlc->magic == HDLC_MAGIC && tty == n_hdlc->tty) {
+		/* queue current process into any wait queue that */
+		/* may awaken in the future (read and write) */
+#if LINUX_VERSION_CODE < VERSION(2,1,89)
+		poll_wait(&n_hdlc->read_wait, wait);
+		poll_wait(&n_hdlc->write_wait, wait);
+#else
+		poll_wait(filp, &n_hdlc->read_wait, wait);
+		poll_wait(filp, &n_hdlc->write_wait, wait);
+#endif
+		/* set bits for operations that wont block */
+		if(n_hdlc->rx_buf_list.head)
+			mask |= POLLIN | POLLRDNORM;	/* readable */
+		if(tty->flags & (1 << TTY_OTHER_CLOSED))
+			mask |= POLLHUP;
+		if(tty_hung_up_p(filp))
+			mask |= POLLHUP;
+		if(n_hdlc->tx_free_buf_list.head)
+			mask |= POLLOUT | POLLWRNORM;	/* writable */
+	}
+	return mask;
+}	/* end of n_hdlc_tty_poll() */
+
+#endif
+
+/* n_hdlc_alloc()
+ * 
+ * 	Allocate an n_hdlc instance data structure
+ *
+ * Arguments:		None
+ * Return Value:	pointer to structure if success, otherwise 0	
+ */
+static struct n_hdlc *n_hdlc_alloc (void)
+{
+	struct n_hdlc	*n_hdlc;
+	N_HDLC_BUF	*buf;
+	int		i;
+	
+	n_hdlc = (struct n_hdlc *)kmalloc(sizeof(struct n_hdlc), GFP_KERNEL);
+	if (!n_hdlc)
+		return 0;
+
+	memset(n_hdlc, 0, sizeof(*n_hdlc));
+
+	n_hdlc_buf_list_init(&n_hdlc->rx_free_buf_list);
+	n_hdlc_buf_list_init(&n_hdlc->tx_free_buf_list);
+	n_hdlc_buf_list_init(&n_hdlc->rx_buf_list);
+	n_hdlc_buf_list_init(&n_hdlc->tx_buf_list);
+	
+	/* allocate free rx buffer list */
+	for(i=0;i<DEFAULT_RX_BUF_COUNT;i++) {
+		buf = (N_HDLC_BUF*)kmalloc(sizeof(N_HDLC_BUF),GFP_KERNEL);
+		if (buf)
+			n_hdlc_buf_put(&n_hdlc->rx_free_buf_list,buf);
+	}
+	
+	/* allocate free rx buffer list */
+	for(i=0;i<DEFAULT_TX_BUF_COUNT;i++) {
+		buf = (N_HDLC_BUF*)kmalloc(sizeof(N_HDLC_BUF),GFP_KERNEL);
+		if (buf)
+			n_hdlc_buf_put(&n_hdlc->tx_free_buf_list,buf);
+	}
+	
+	/* Initialize the control block */
+	n_hdlc->magic  = HDLC_MAGIC;
+
+	n_hdlc->flags  = 0;
+	n_hdlc->read_wait  = NULL;
+	n_hdlc->write_wait = NULL;
+	
+	return n_hdlc;
+	
+}	/* end of n_hdlc_alloc() */
+
+/* n_hdlc_buf_list_init()
+ * 
+ * 	initialize specified HDLC buffer list
+ * 	
+ * Arguments:	 	list	pointer to buffer list
+ * Return Value:	None	
+ */
+void n_hdlc_buf_list_init(N_HDLC_BUF_LIST *list)
+{
+	memset(list,0,sizeof(N_HDLC_BUF_LIST));
+		
+}	/* end of n_hdlc_buf_list_init() */
+
+/* n_hdlc_buf_put()
+ * 
+ * 	add specified HDLC buffer to tail of specified list
+ * 	
+ * Arguments:
+ * 
+ * 	list	pointer to buffer list
+ * 	buf	pointer to buffer
+ * 
+ * Return Value:	None	
+ */
+void n_hdlc_buf_put(N_HDLC_BUF_LIST *list,N_HDLC_BUF *buf)
+{
+	unsigned long flags;
+	spin_lock_irqsave(&list->spinlock,flags);
+	
+	buf->link=NULL;
+	if(list->tail)
+		list->tail->link = buf;
+	else
+		list->head = buf;
+	list->tail = buf;
+	(list->count)++;
+	
+	spin_unlock_irqrestore(&list->spinlock,flags);
+	
+}	/* end of n_hdlc_buf_put() */
+
+/* n_hdlc_buf_get()
+ * 
+ * 	remove and return an HDLC buffer from the
+ * 	head of the specified HDLC buffer list
+ * 	
+ * Arguments:
+ * 
+ * 	list	pointer to HDLC buffer list
+ * 	
+ * Return Value:
+ * 
+ * 	pointer to HDLC buffer if available, otherwise NULL
+ */
+N_HDLC_BUF* n_hdlc_buf_get(N_HDLC_BUF_LIST *list)
+{
+	unsigned long flags;
+	N_HDLC_BUF *buf;
+	spin_lock_irqsave(&list->spinlock,flags);
+	
+	buf = list->head;
+	if (buf) {
+		list->head = buf->link;
+		(list->count)--;
+	}
+	if (!list->head)
+		list->tail = NULL;
+	
+	spin_unlock_irqrestore(&list->spinlock,flags);
+	return buf;
+	
+}	/* end of n_hdlc_buf_get() */
+
+/* init_module()
+ *
+ *	called when module is loading to register line discipline
+ * 	
+ * Arguments:		None
+ * Return Value:	0 if success, otherwise error code
+ */
+int init_module(void)
+{
+	static struct tty_ldisc	n_hdlc_ldisc;
+	int    status;
+
+	printk("HDLC line discipline: version %s\n", szVersion);
+
+	/* Register the tty discipline */
+	
+	memset(&n_hdlc_ldisc, 0, sizeof (n_hdlc_ldisc));
+	n_hdlc_ldisc.magic		= TTY_LDISC_MAGIC;
+#if LINUX_VERSION_CODE >= VERSION(2,1,28)
+	n_hdlc_ldisc.name          	= "hdlc";
+#endif
+	n_hdlc_ldisc.open		= n_hdlc_tty_open;
+	n_hdlc_ldisc.close		= n_hdlc_tty_close;
+	n_hdlc_ldisc.read		= n_hdlc_tty_read;
+	n_hdlc_ldisc.write		= n_hdlc_tty_write;
+	n_hdlc_ldisc.ioctl		= n_hdlc_tty_ioctl;
+#if LINUX_VERSION_CODE < VERSION(2,1,23)
+	n_hdlc_ldisc.select		= n_hdlc_tty_select;
+#else
+	n_hdlc_ldisc.poll		= n_hdlc_tty_poll;
+#endif
+	n_hdlc_ldisc.receive_room	= n_hdlc_tty_room;
+	n_hdlc_ldisc.receive_buf	= n_hdlc_tty_receive;
+	n_hdlc_ldisc.write_wakeup	= n_hdlc_tty_wakeup;
+
+	status = tty_register_ldisc(N_HDLC, &n_hdlc_ldisc);
+	if (!status)
+		printk (KERN_INFO"N_HDLC line discipline registered.\n");
+	else
+		printk (KERN_ERR"error registering line discipline: %d\n",status);
+
+	if (status)
+		printk(KERN_INFO"N_HDLC: init failure %d\n", status);
+	return (status);
+	
+}	/* end of init_module() */
+
+/* cleanup_module()
+ *
+ *	called when module is unloading to unregister line discipline
+ * 	
+ * Arguments:		None
+ * Return Value:	None
+ */
+void cleanup_module(void)
+{
+	int status;
+	/* Release tty registration of line discipline */
+	if ((status = tty_register_ldisc(N_HDLC, NULL)))
+		printk("N_HDLC: can't unregister line discipline (err = %d)\n", status);
+	else
+		printk("N_HDLC: line discipline unregistered\n");
+}
FUNET's LINUX-ADM group, linux-adm@nic.funet.fi
TCL-scripts by Sam Shen (who was at: slshen@lbl.gov)